How the brain integrates kinesthetic information about self-generated movements with other sensory signals caused by those movements is largely unknown. While there is a substantial and growing body of research on how the brain integrates multiple sensory signals generated by objects and events in the world, much less is known about how the brain integrates kinesthetic and visual motion signals. Even less is known about how the interactions between kinesthesis and vision change with age. The current proposal addresses these gaps in our understanding, specifically aiming to elucidate how kinesthetic signals generated by one's hand motion influence visual motion processing and how those interactions change with age - a question of clinical significance because of the known age-related deficits in visual motion processing. The first aim focuses on an aspect of multisensory integration that is often overlooked - how the brain determines whether or not, or how strongly, to couple signals from different modalities (most current research focuses on how the brain weights different signals when they are perfectly coupled). We will measure how subjects adapt their inter-modal coupling to changes in signal reliability and compare subjects' performance to that of optimal Bayesian models that are parameterized by estimates of individual subjects' sensory uncertainty. The models provide a tool for testing the hypothesis that aging leads to changes in multimodal integration mechanisms themselves, by allowing us to discount the effects of changes in unimodal signal uncertainty on older subjects' behavior. The second aim will study whether and how the brain uses kinesthetic signals to support and enhance early visual processing and how this changes with age. In one set of experiments, we will test the hypothesis that predictive signals associated with kinesthesis enhance the detectability of congruent visual motion signals and measure the tuning of this enhancement to conflicts between the signals. Another set of experiments will test a strong version of the interaction hypothesis - that kinesthesis can be solely sufficient to generate visual motion percepts. Here, we will expand on a phenomenon discovered in our preliminary studies - that many subjects report seeing visual motion embedded in a white noise field optically collocated with their moving hand. To quantify the strength of generated motion percepts, we will experimentally determine the real visual motions that perceptually match reported phantom motions. We will further explore this kinesthetic enhancement of visual processing to determine whether the underlying interactions between kinesthesis and visual motion processing are multiplicative or additive. A final set of experiments will test the hypothesis that the brain uses kinesthetic signals to aid in motion segmentation by both enhancing the motion signal from a moving target when the hand moves the target and by suppressing the background when the hand moves it. We will measure age-related changes for each of these three forms of interaction between kinesthesis and vision; matching signal uncertainty for young and older subjects to isolate changes that are result from age-related changes in multisensory integration mechanisms.